1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device having an improved attachment of a liquid crystal panel for improving a sealing force of a sealing material.
2. Description of the Related Art
In general, a liquid crystal display (LCD) device is a transmission-type flat panel display device adaptable to various electronic instruments, such as mobile phones, personal digital assistants (PDAs), notebook computers, and lap-top computers. Because of their light weight, thin profile, compact size, and high picture quality, the LCD device is advantageous as compared to other flat panel display devices. Generally, the LCD device can be categorized based upon its method for manipulating liquid crystal molecules. Presently, a thin film transistor (TFT) LCD device is commonly used due to its relatively fast reaction speed and low residual image.
FIG. 1 is a plan view of a liquid crystal display device according to the related art. In FIG. 1, a TFT LCD 1 includes a lower substrate 3, an upper substrate 5, and a liquid crystal material layer 17 formed between the lower substrate 3 and the upper substrate 5. Gate lines 11 are arranged along a first direction on the lower substrate, and data lines 13 are arranged along a second direction perpendicular to the gate lines on the lower substrate. Intersections of the gate and data lines 11 and 13 define a plurality of pixel regions. The gate lines 11 and the data lines 13 are electrically connected to external drive devices (not shown) through pads 12 and 14, respectively, that are formed along a non-displaying region of the lower substrate 3. As a scan signal is applied to each pixel through the gate line 11, a corresponding TFT 15 is enabled to supply an image signal input through the data line 13 to the liquid crystal material layer 17.
A sealing region 7 is formed along marginal portions of the lower substrate 3 and the upper substrate 5, and a sealing material 22 is deposited on the sealing region. Accordingly, the lower substrate 3 and the upper substrate 5 are attached by the sealing material 22. In addition, a black matrix 9 and a light shielding element (not shown) are formed at the sealing region 7 to prevent light transmission to the sealing region 7, wherein the black matrix 9 is formed at the upper substrate 5. The sealing region 7 includes liquid crystal injection opening 20 for injecting liquid crystal material between the lower substrate 3 and the lower substrate 5 after they are attached. After the liquid crystal material is injected through the liquid crystal injection opening 20, the liquid crystal injection opening 20 is encapsulated by an encapsulation material. Since the encapsulation material is commonly made of a photosensitive material, after the encapsulation material is filled in the liquid crystal injection opening 20, ultraviolet light is irradiated thereto to harden the encapsulation material. In addition, the TFT LCD 1 includes a metal layer 24 formed along the marginal portions of the substrate to electrically interconnect the gate line 11 and the data line 13 to the pads 12 and 14, respectively, and to external drive circuits (not shown).
FIG. 2 is a cross sectional view of a pixel region and a sealing region of the liquid crystal display device along I-I′ of FIG. 1 according to the related art. In FIG. 2, a gate electrode 31 is formed on the lower substrate 3 of the pixel region, and a gate insulation layer 32 is stacked over the lower substrate 3. A semiconductor layer 34 is formed on the gate insulation layer 32, and as a scan signal is applied to the gate electrode 31, the semiconductor layer 34 is activated to form a channel layer between source/drain electrodes 36. As the semiconductor layer 34 is activated, a data signal is input to the source/drain electrodes 36 through the data line 13.
An inorganic passivation layer 39 made of an inorganic substance is formed on the source/drain electrode 36, and an organic passivation layer 37 made of an organic substance having a low dielectric constant, such as a photo acryl or Benzocyclobutene (BCB) is formed on the inorganic passivation layer 39. Formation of the organic passivation layer 37 allows for implementation of a high aperture ratio, whereby a liquid crystal display device with a flat surface can be fabricated.
A pixel electrode 38 made of a transparent material such as Indium Tin Oxide (ITO) is formed on the organic passivation layer 37 and is electrically connected to the source/drain electrodes 36 through the contact hole 61 formed at the inorganic passivation layer 39 and the organic passivation layer 37. Although not shown, an alignment layer is deposited on the organic passivation layer 37 to align the liquid crystal molecules of the liquid crystal material layer 17.
The black matrix 9 and a color filter layer 42 for implementing color are formed on the upper substrate 5. The black matrix 9 is made of Cr, CrOx, and Cr/CrOx, and is formed at the TFT region of the pixel region near the gate and data lines by the sealing region. In addition, a common electrode (not shown) is formed on the black matrix 9 and the color filter layer 42, whereby an electric field is formed between the common electrode and the pixel electrode to drive the liquid crystal molecules of the liquid crystal material layer 17. The alignment layer (not shown) is formed on the common electrode to align the liquid crystal molecules.
A plurality of spacers 50 are distributed between the lower substrate 3 having the TFT formed thereon and the upper substrate 5 having the color filter layer 42 formed thereon to maintain a uniform cell gap. In addition, after the lower substrate 3 and the upper substrate 5 are sealed, the liquid crystal material is injected into the cell gap through the liquid crystal injection opening 20 (in FIG. 1) to form the liquid crystal material layer 17.
FIG. 3A is a plan view of a sealing region of a liquid crystal display device according to the related art, and FIG. 3B is a cross sectional view taken along I-I′ of FIGS. 1 and 3A. In FIGS. 3A and 3B, a plurality of openings 62 are formed in the inorganic passivation layer 39 and the organic passivation layer 37 between the plurality of metal layers 24 that are formed on the gate insulation layer 32. Accordingly, when the sealing material 22 is deposited within the sealing region 7 (in FIG. 1), the sealing material 22 fills the opening 62. If no openings 62 were provided, the sealing material 22 for attaching and sealing the liquid crystal panel would be directly deposited on the organic passivation layer 37. However, organic substances, such as photo acryl or BCB, and the sealing material do not easily bond together. Accordingly, if the liquid crystal panel is attached by depositing the sealing material 22 on the organic passivation layer 37, the sealing would be broken due to weak adhesion forces, thereby causing the injected liquid crystal material to leak into the liquid crystal panel.
Adhesion forces between inorganic substances, such as SiNx, and the sealing material are known to be relatively good. Accordingly, the opening 62 is formed at the inorganic passivation layer 39 and the organic passivation layer 37 between the metal layers 24 to expose the gate insulation layer 32, which is made of an inorganic substance. Then, the sealing material 22 is filled on the gate insulation layer 32 to directly attach a portion of the sealing material 22 onto the gate insulation layer 32, thereby seeking strengthening of adhesion force of the liquid crystal panel. In addition, the openings 62 of the sealing region 7 (in FIG. 1) is simultaneously formed when the contact hole 61 of the pixel region is formed.
However, although the adhesion force of the liquid crystal panel is improved by forming the openings 62 at the inorganic passivation layer 39 and the organic passivation layer 37 between the metal layers 24, bonding of the liquid crystal panel is problematic. For example, glass fibers are mixed within the sealing material 22, and the openings 62 formed between the metal layers 24 narrow along a direction toward the gate insulation layer 32. Accordingly, a width of the openings 62 near the gate insulation layer 32 is very small and may become clogged due to the glass fibers. Thus, the sealing material 22 would not completely fill the openings 62 to contact the gate insulation layer 32, thereby reducing the adhesion forces of the liquid crystal panel.